The present invention relates to a liquid crystal display (LCD) and method of manufacturing thereof, and, in particular, to a structure of a barrier wall for forming an alignment film of an LCD, and a method for forming the alignment film.
Liquid crystal displays (LCDs), particularly, thin film transistor LCDs (TFT LCDs) have become the main products of the flat displays presently available in the market. The TFT LCD has become an important display platform for the present information appliance and audio/video system.
A TFT LCD basically includes an array substrate, a color filter and a liquid crystal layer located between the array substrate and the color filter. When the characteristics of electrical field between the array substrate and the color filter change, the liquid crystal molecules in the liquid crystal layers which guides light transmission from the array substrate to the color filter are twisted with different degrees so that light with different intensities can reach the color filter, thereby to display a desired image.
To enable the liquid crystal molecules in the liquid crystal layer to have a predetermined orientation, an alignment film is applied on one or each of the array substrate and color filter. Then grooves are formed in the alignment film to form an alignment layer. The alignment film is made of liquid polyimide (PI) which is applied to the array substrate and/or color filter by ink-jet printing. To prevent the liquid PI from diffusing too quickly which may contaminate a sealant for hermetically connecting the array substrate and the color filter together, an alignment film barrier wall is formed between the sealant and an active area of the substrate. The barrier wall is made of polystyrene (PS) and has a height which can be as large as tenfold of a thickness of the alignment film.
Referring to FIG. 1A, a barrier wall 10 is formed on a color filter 12. Liquid PI 14 is applied to the color filter 12 and flows toward the barrier wall 10 along a direction indicated by an arrow 16. The barrier wall 10 is a straight, flat wall perpendicularly erected from the color filter 12. The liquid PI 14 is applied to a top surface of the color filter 12 through multiple injection points.
Referring to FIG. 1B, when the liquid PI 14 reaches the barrier wall 10, it is blocked by the barrier wall 10. A large reaction force is exerted by the barrier wall 10 to the liquid PI 14, which causes the liquid PI 14 to flow upwardly and backwards as indicated by an arrow 18.
Referring to FIG. 1C, the liquid PI 14 which flows backwards cannot evenly extend over the top surface of the color filter 12, but accumulates at a place near the barrier wall 10, resulting in that the alignment film has an uneven thickness. Such an uneven thickness of the alignment film can cause the TFT LCD to have problems of gap mura. Accordingly, the yield rate of the TFT LCD is adversely affected and low.
In addition, for the straight, flat, perpendicularly erected barrier wall 10 of the prior art, the injected liquid PI 14 has the possibility of overflow through the barrier wall 10 if the injection speed of the liquid PI 14 is not well controlled. When this happens, the liquid PI 14 can reach the sealant to contaminate the sealant, which may result in a peeling-up of the sealant.
Accordingly, it is needed to provide a barrier wall for an alignment film and a method for manufacturing an alignment film, in order to solve the problems of the prior art.